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The structure and functionalities of rice bran protein (RBP) oxidized by peroxyl radicals were analyzed in this study. The thermal decomposition of 2,2′-azobis [2-amidinopropane] dihydrochloride (AAPH) was used to generate peroxyl radicals. Increased oxidation of RBP by AAPH gradually generated more carbonyl (COOH) groups, which resulted in a loss of protein sulfhydryl groups. Low oxidization (≤0.2 mmol/L AAPH) could cause structural unfolding with an increase in surface hydrophobicity and emulsion properties but reducing the solubility and disulfide bonding. Moderate and high oxidization (>0.2 mmol/L AAPH) could result in soluble aggregates formed by subunits with molecular weights of 53, 49, and 36 kDa, attributed to globulin, albumin, and glutelin, increasing the solubility and disulfide bonding but decreasing the surface hydrophobicity and emulsion stability. Oxidization by low concentration AAPH induced a more unordered structure and transformation from β-turn to β-sheets, while a more ordered structure increased with aggregation.